The invention relates to a radio method for doors.
Numerous and diverse requirements are imposed on a radio method for doors, especially when individual components that execute the radio method are battery-powered.
To ensure a long useful life for the battery, one requirement to be met by a radio method for doors is that the radio method is permitted to have only a small energy demand.
Since standard practice for battery-powered components is to activate such components only as needed, a radio method for doors must be capable of establishing a connection between the battery-powered component and the stationary door controller quickly and reliably, while at the same time ensuring that the connection is established exclusively between the stationary door controller and the mobile units allocated thereto and not with components that by chance are also within its radio-sensing range, as could be the case, for example, of mobile units of a door controller present in the vicinity or of other radio systems that by chance are present in the vicinity, such as mobile telephones or mobile computer systems equipped with WLAN or Bluetooth transmitter/receiver systems.
Since safety-related data, such as detection of an obstruction in the zone of the door, can also be transmitted with a radio method for doors, data exchange must be possible rapidly and must be largely immune to interferences from the surroundings, for example due to other radio systems.
In order to ensure safe operation of a door, especially when the door is a high-speed door that moves at 1 to 2 meters per second, for example, a radio method for doors must be able to transmit safety-related data in real time, which in this case means a necessary reaction time of less than 5 ms.
In order to comply with the diverse legal basic conditions that exist throughout the world for operation of radio systems, it is important for a cost-effective radio method for doors that the radio method use a frequency band that is approved for unlicensed operation of radio systems in almost all countries. Consequently, however, the radio method must be designed such that it also operates reliably in coexistence with other radio services that use the same frequency band.
A further requirement imposed on a radio system for doors is that the needed hardware components be as inexpensive as possible and ensure high reliability for many years of operation on the door.
From the prior art there are already known several solutions in which, for example, a battery-powered transmitter or a transmitter/receiver is mounted on the safety strip of a door in such a way that it can communicate unidirectionally or bidirectionally with a door controller via a radio link.
As an example, DE 10000641 C1 describes a device for motor-driven doors, wherein the measured values delivered by the safety strip are communicated by radio to a stationary door controller that receives these radio signals. To ensure the necessary safety, this device is equipped with two transmitters, in order to transmit the information redundantly at different frequencies to the door controller. However, this device has the disadvantage that it needs two independent transmitters on the safety strip, making it complex and expensive, and that the transmitters do not have the ability to adjust to a different transmission frequency if the transmission channel that they are using is being used by another radio system or is otherwise faulty. Furthermore, this device does not have any features to ensure that the radio signals of the protective device can be processed only by the door controller allocated to them.
Also known from the prior art (DE 10302812 B4) is a device that saves electric energy by waking the riding unit cyclically, in order to detect whether a signal indicating that the stationary door controller is requesting further operation of the riding unit can be measured by the stationary door controller. This prior art device has the disadvantage that the riding unit cannot distinguish whether the received signal originates from the door controller allocated to it or from another transmitter. Thus undesired activation of the riding unit can occur easily, thus negatively affecting the battery life. Furthermore, this prior art also does not provide any indication as to how reliable operation can be ensured if further radio systems are present in its zone of action.
From the prior art (U.S. Pat. No. 4,027,276) there is known a radio system for a door wherein a receiving device is capable of receiving and separating the signals of a plurality of transmitting devices. For this purpose, the transmitting device is equipped with means whereby a 200 megahertz (MHz) to 400 MHz transmitted signal can deliver, via an electronic circuit, an encoded signal in the form of pulses, and with a receiving device that can receive the signals encoded in this way and identify the device from which the signal was sent on the basis of the coding. This prior art device has the disadvantage that the specified frequencies and encoding make high-speed data transmission impossible and that a collision of a plurality of transmitted signals sent out simultaneously cannot be separated by the receiving device, thus potentially causing breakdown of data transmission.
Also described in the prior art (EP 1722339 A1) is a method for ensuring, by alternating transmission, reception and checking of identification numbers between a stationary unit and a mobile unit, that each communication partner has received the respective information intended for it. This method also has the disadvantage of not providing any steps for ensuring reliable communication in the case of collision of a plurality of transmitters that are transmitting simultaneously on the same channel.
Also known from the prior art are the three radio systems known as WLAN (wireless local area network), Bluetooth and ZigBee, all of which operate with different technical features in the 2.4 gigahertz (GHz) frequency band, which is unlicensed almost throughout the world.
WLAN, whose features are specified in IEEE Standard 802.11 and which is specified mainly for wireless networking of personal computers at data rates of up to 54 megabits per second for high-speed data communication over distances of up to 300 meters, uses 11 or 13 static channels, albeit overlapping in the frequency spectrum, within the frequency band between 2.4 GHz and 2.4835 GHz. Of these channels, only three channels respectively do not overlap. Consequently, a disadvantage for use in radio systems for doors exists in that, for practical purposes, only three WLAN networks can be operated concurrently in immediate proximity. Furthermore, because of their high transmitting power and high data-transmission rates, WLAN radio systems have high power consumption and use relatively lengthy control information (known as headers) in the data packets, thus negatively impacting the required high-speed data transmission (short reaction time) and thus the use as a radio method for doors.
The radio system according to the ZigBee standard also operates in the 2.4 GHz frequency band, is intended for the use of wireless radio switches and radio sensors and should ensure a long battery life. ZigBee is designed for short ranges (10 to 75 meters) and is based on IEEE Standard 802.15.4. ZigBee uses 25 static channels within the 2.4 GHz frequency band. The disadvantages of ZigBee in a radio method for doors are that only a relatively low data-transmission rate of at most 250 kilobits per second is achieved and the response times are approximately 5 milliseconds (ms), which does not allow a rapid reaction to a dangerous situation of the door. Furthermore, at most 16 ZigBee channels can be operated concurrently in an interference-free environment, thus imposing a further restriction for large door systems, such as in a freight center. Because ZigBee uses static channels, devices networked with ZigBee cannot switch dynamically to an alternate channel if the preset channel is disturbed or blocked by another radio system, such as a mobile WLAN device. Certainly methods for dynamic frequency adaptations are also planned for ZigBee, but they are designed for reaction times of much longer than 10 ms.
Protocol frames of different lengths can be used for data transmission in ZigBee. According to the ZigBee standard, however, a protocol frame comprises at least one 8-byte address, one 5-byte preamble and one 2-byte checksum, and so its length is at least 15 bytes regardless of the useful information to be transmitted. This has the disadvantage that the time for transmission of short useful information, for example of 1 byte to 4 bytes, is a multiple of what is actually necessary for transmission. In addition, with a net data rate of 250 kilobits per second (kbps), data transmission takes place relatively slowly compared with the frequency band being used.
With the Bluetooth standard, which also belongs to the prior art, is specified in IEEE 802.15.1 and is intended for short-range radio networking of small mobile devices such as mobile telephones and PDAs with one another or with stationary computers and peripherals, a range up to 100 meters can be achieved with a 100-milliwatt transmitter. Bluetooth divides the available frequency band between 2.402 GHz and 2.480 GHz into 79 channels 1 MHz apart, and switches between them in a defined frequency hopping routine up to 1600 times per second, or in other words every 0.625 ms, and so a frequency hop already takes place within one communication cycle, or in other words between the end of the incoming data transmission and the beginning of the response. As regards a radio method for doors, Bluetooth has the disadvantage that it needs a relatively large processor capacity due to the rapid frequency hopping and thus has high power demand and needs expensive components, which is not compatible with long battery life. Furthermore, the process of synchronization between two Bluetooth communication partners lasts several seconds, thus preventing use for a door. Furthermore, it cannot be ruled out that interactions with other Bluetooth devices—such as mobile telephones—not allocated to the door may occur when these devices are in the sensing zone of the door. Certainly version 2.0 of Bluetooth provides the ability to select the channels being used by the frequency hopping method, for example by blocking individual channels. However, the criteria according to which this selection will be made is not specified.
In the Bluetooth standard, a protocol frame comprises at least a 9-byte access code, a 7-byte header, a 1-byte data header and a 2-byte checksum. Thus the protocol frame comprises at least 19 bytes regardless of the useful information to be transmitted, and thus is not compatible with high-speed data transmission of short useful information.
Furthermore, the frequency-hopping method of Bluetooth and the other known radio systems has the disadvantage that these systems unconditionally execute the frequency hops according to an internally defined sequence or to the random selection principle, and only after the frequency hop to the next channel do they check whether the channel is free at all for its own data transmission. This has the disadvantage that sometimes these systems may not transmit any data for a period longer than 100 ms, for example, since they are continuously hopping to already occupied channels. Hereby these systems are greatly restricted as regards use in transmission of safety-related data of a door and as regards the associated requirement of a rapid reaction time.